Hello Makers lets collaborate on this platform to build a Contact-Less Thermometer. I know the fabrication (even the frugal fabrication) during this lockdown period may not be possible due to inaccessibility/non-availability of the required supplies but lets together work on the project upto “Digital Pre-Fabrication” stage. This may help us to fabricate the device soon after the lockdown period when supplies are available and it may also help those who have access to these supplies and facilities during lockdown period.
So we all have seen this Contact-Less Thermometer atleast in news and social media videos under this pandemic situation due to COVID-19 spread. Doctors, Police men, Checking staff at places such as Airports, Hospitals, Roads and various other organizations, they are using it to check (screening) the people’s body temperature by just pointing this gun like structure at their forehead and getting the temperature without making any physical touch.
It is very important to work on building of such devices and help other to build these devices by their own due to many reasons but below two are on the top in my views.
We need to increase the sampling rate by testing the body temperature of as many people, which requires large number of such device units.
Most Commercial companies of such products are trying to increase the price (price-gouging) which will at some rate making these products inaccessible.
The contact-less thermometer (why we need contact-less, we all are aware) basically is a infrared thermometer which measures the surface temperature of an object. Anything with mass (eg: Human body, objects) emits some kind of energy in the form of heat ie infrared rays (IR). The infrared thermometer measures the difference between the surrounding IR and the IR coming from the object to determine the surface temperature of object itself.
I will talk more technically on the working principle (must to know for developing the device) little later. One can read more about its working on these links:
Which sensor are these? Found this nice project which uses MLX90614 sensor for making the non-contact temperature sensor. The range of this is (-70 C to 382 C) with an accuracy of ±0.02 C. Also, I have curated other interesting work done by different people which might be helpful.
Yes we can make one with the plain diode too. Given that the range of measurement for our use is very small, one does not need the range or resolution of the MLX90614. However this requires one to add several additional components to make the plain diode work well.
If the MLX90614 is available use it. It will probably be faster to design but much more expensive Rs.1300/- per unit. Else use the plain diodes which is Rs.200/- per unit.
The ADC is to convert the analog voltage into a digital value. One could also simply drive a anolg moving coil meter and obtain a reading.
The DSP filters out dark current - a type of noise when no signal is present, and transients. It also has factory calibrated values loaded into it’s memory. If such memory is not available, one has to use a preset and adjust it. Having low temprature drift presets is exceedingly hard. Hint: chotubot adjustment.
Exactly @ravi312 this (MLX90614) is the sensor which i have selected for this project, i will be posting the the complete section on its technical specification and mean while you can help in design the 3D model for this, i am also working on it.
@ravi312 i think need to do a fresh start for (Laser cutter) design as the design which i am currently doing also need much changes, I mean need to rethink the design to be in bits and pieces and easy to assemble. Lets discuss on it.
But still for the things done so far please find the file below.
[ This morning i first checked the internet speed and just smiled because it was very low yesterday might be due to rain fall happend day before yesterday night. I use my mobile internet via hotspot.]
Building Contact-Less Thermometer
Section One: Sensor Selection and its datasheet Reading.
I found sensor MLX90614 is suitable for our development as this itself is an IR Thermometer in a TO-39 package.
On searching its availability online I found the lowest price from the following vendor.
Lets get into the details of this sensor.
MLX90614 (An IR Thermometer)
This sensor is basically the combination of IR Sensitive thermopile detector chip (part number: MLX81101) and signal conditioning ASSP (MLX90302), therefore it reduces all the core complexity for detecting and measuring the temperature and thus allowing us to focus only on reading the measurements form its memory location and putting it on a small display.
In fact this IR Thermometer is also Factory Calibrated in wide temperature
range: -40°C…+125˚C for sensor temperature and -70°C…+380˚C for object temperature.
Measurement Resolution of 0.02*Celecius (This is the least measurement count).
High Accuracy of 0.5*Celcius.
Note: Lets understand working of this sensor more technically as I stated earlier.
IR Thermometer focuses on the light coming from the object in the form of Infrared (IR) rays and channelize this IR radiation to the detector which is known as Thermopile. Inside this Thermopile IR radiation is turned into heat which then turned into electricity.
The electric signal generated by IR Thermopile is passed to signal conditioning unit specially designed to process it. This unit basically amplify the signal, then covnvert it to stream of bits (using 17 bit ADC) and then fed it to DSP (digital signal processor) where signal is treated with FIR and IIR low pass filters for further reduction of the band width of the input signal to achieve the desired noise performance and refresh rate. The output of IIR filter is the measurement results.
Based on this measurement results, the object temperature To and ambient temperature Ta is calculated and get stored in two dedicated location of RAM, which can be read via I2C interface or via the PWM digital output.
The measured value is the average temperature of all objects in the Field Of View (FOV) of the sensor.
Interfacing (Connecting) to Microcontroller/Arduino Board: There are two methods for it
I2C Two-Wire Protocol.
10-bit PWM Output.
In this development we will use I2C Two-Wire Protocol.
Some very important point to be consider while development as per datasheet.
“ It is very important for the application designer to understand that these accuracies are only guaranteed and achievable when the sensor is in thermal equilibrium and under isothermal conditions (there are no temperature differences across the sensor package). The accuracy of the thermometer can be influenced by temperature differences in the package induced by causes like (among others): Hot electronics behind the sensor, heaters/coolers behind or beside the sensor or by a hot/cold object very close to the sensor that not only heats the sensing element in the thermometer but also the thermometer package.”
Thus we need to carefully design the placement of electronics inside the encloser.
We can also discuss other datasheet parameters which you think may be essential for our development.
@ravi312 as we are proceeding for the designing the encloser with multiple parts (basically to get laser cut) i am thinking of adding below assembly element/mechanism to the deisgn of IR Thermometer encloser. This mechanism will make assembling and disassembling of parts easy.
We can also work on other assembling mechanism design which makes it more simple.
The use of thermopile sensing eliminates the need of complext lens coating typical of IR photodiode sensing.
The advantage of photodiode is the ability to sense multiple wavelengths of IR. With photo diodes typically one would have as rerence a blackbody embedded inside the device. A Second diode will be placed near this black body and sense it’s temprature. Since this body is at ambient temprature, one can subtract ambient from the main sensing diode, thereby making it substantially independent of the medium between target and the probe.
For our use case the thermopile is wholly a better fit.
We can decide on the locking mechanism and making it modular once we have a rough idea of components we are going to use.
Let’s brainstorm the casing design. Do we want a gun-style detector or a simple torch style would be good to go?
I think I would prefer the one which has minimal moving parts and as you said earlier, easy to assemble.
If you have other designs, feel free to share.
Here is a torch style one
Dont make it a tubular structure. Both assembly and disassembly becomes difficult. Instead make the bottom long section removable. Use machine screws and nuts. Self tapping wear out the holes quite quickly.
I have divide this section into two subsections and they are
Section 2.1: Defining Features of this device.
Section 2.2: Making Block Diagram.
Section 2.1: Defining Features of this device.
To design and develop any device it is very important to define the purpose and features of that device. Purpose tells about what that device will actually do and features define the set of capabilities and services of the device required to achieve that purpose easily by the user.
Purpose: This device will measure the surface temperature of an object and display it on the small screen and also provide the same data over internet if needed.
Non-contact, precise, fast, safe and easy to use.
There are many situations and applications where we need to measure the temperature of an object at distance. Such as measuring the human body temperature without touch it in the current situation of Epidemic COVID_19.
And also in applications like measuring the temperature of hot and cold things in the kitchen, temperature of some moving part in some plant, detecting heat insulation breakages and many other commercial and industrial applications.
Thus we require these measurements to be non-contact, easy, precise and fast enough. For which i have decide to use MLX90614 (IR Thermometer Sensor Module). We have already discussed the details of it and one can find it below.
Readings on OLED Display.
To display reading and other data a small display is essential.
I have selected Oled 128x64 screen.
The data is also required over internet. One of it application is to generate Heat Map.
Two methods to achieve this, either interface a WiFi module (use internet through the nearby WiFi network) or GSM/GPRS module (use mobile network through SIM) to the processing device.
For this version i have decided to go with WiFi module.
Laser pointer for easy targeting the surface of an object.
laser pointer will provide the sight for accurate targeting the surface of an object for temperature measurement.
Low power laser module is required for this.
Real Time Clock.
Date and Time stamp on the screen. This may be kept optional but i would like to add this.
I have selected RTC DS3231.
Battery makes a device very convenient to use.
For this version i am only thinking of using replaceable 9 volt battery and will wok on rechargeable battery with designing inbuilt battery management system (BMS) later (but yes very much needed).
Aesthetically designed encloser.
The encloser must be designed aesthetically handy, lightweight, compact and also order to accommodate all modules, PCB and components.
Encloser internal temperature measurement.
It is very important to also monitor the encloser internal temperature for the following reason.
Section 2.2: Making Block Diagram.
With the features of the device we have also talked on the most of its components/modules to be used in this development. Now time to decide for its processing unit, I have figured out two options for this.
Arduino Pro Mini
lets look the block diagram of this device using both the options and then will get into details of each.
Block Diagram using Arduino Pro Mini as a Processing Unit
So the main difference we found in above two block diagrams is that with Arduino Pro Mini we need to interface external WiFi module (ESP 01) to communicate over internet.
While with NodeMCU (ESP-12E), there is no requirement to interface any external WiFi module because it has inbuit WiFi.
Lets also tabulate all important operational parameters of Arduino Pro Mini and NodeMCU (ESP-12E).
Arduino Pro Mini
80 to 160 Mhz
External WiFi Module Interface required.
3.3v and 5v both options available but then Clock Freq will be 8 Mhz and 16 Mhz respectively.
Here NodeMCU is much powerful as compared to Arduino Pro Mini. But Please note the specification of Arduino Pro mini is also good enough for this device development.
To know more about Arduino Pro Mini and NodeMCU please refer to below links:
Now i would like to draw attention to very important parameter that is current requirement, all modules are same except Arduino needs external WiFi Module and NodeMCU has in built.
So lets look for the figure of Overall current requirements for both the cases.
Overall Current Consumption = WiFi (RF Transmission) Current requirement + Total current of Modules
Arduino Pro mini
In this case external Wifi Unit consumes around: 450 mA to 600 mA.
Overall Current Consumption = 600 mA + 97.210mA =697.210mA
In this its inbuit WiFi consumes around: 80 mA.
Overall Current Consumption = 80mA + 97.210mA = 177.210 mA
There is huge difference as per current consumption, Therefore NodeMCU (ESP-12E) is the perfect choice for this development.
But we will design the device using both Arduino Pro Mini and NodeMCU.
Looking forward for any addition, modification and suggestion.
With the help of the above block diagrams please try to make circuit diagram of the device. I am trying my best to complete the PCB design as soon as possible. Please find the design done so far given below (its in under development not the final one).
Following this, although photos are not posted here, the PCB design was completed. In a separate discussion, this set off a series of discussions, initially leading from the form factor, which turned out to be a pistol grip design.
The following observations are just a selection, because that discussion went on for over a day.
The pistol form factor was criticised, largely because of the laser pointer, and the fact that the resultant PCB polygon wasted a lot of raw material.
The laser pointer itself seemed unnecessary for this application. This is not a general purpose thermometer, it is a rapid response low cost tool meant to be made and used in the field in order to simplify first level sorting of persons (out of potentially hundreds or thousands every day) who need to be queried on their medical history, in order to isolate them from symptom free persons who might be less of a hazard to fellow workers or public transport users. It is just a tech assist to human sorting, which if done alone might cause huge accumulations of people in public spaces.
2 form factors were debated and discussed 3.1 a simple handheld unibody of regular shape, either rectangular cuboid or slightly rounded 3.2 a 2 piece design, one fitted on the forefinger that basically houses the infrared sensor, and a second clipped to the wrist with the display, drivers and power source.
If this project is to be meaningful, it must be finished quickly, and published to empower as many assemblers, in as many places across the country as possible, in order to support attempts to ease the lockdown and enable hundreds of thousands of people to return to work with the most protection possible.